Gas well deliquification is an important technology for exploitation of mature gas wells. As a gas well matures, the reservoir pressure will decline. As a result thereof, the gas velocity in the production tubing will decrease, which can lead to liquid loading. Liquid loading refers to accumulation of liquid components, such as water and condensed hydrocarbons, in gas wells with insufficient gas flow to lift the accumulated liquid to the wellhead. Liquid loading may cause the well to produce the gas erratically; such as in slug flow or churn flow, at a much lower flow rate. Liquid loading can eventually cause production to cease. Estimated is that about 80% of the approximately 500 000 United States gas wells and about 30% to 40% of the Dutch gas wells are affected by liquid loading. In particular, many offshore wells are abandoned due to liquid loading problems. For this reason, gas well deliquification is used to increase the lifetime of gas wells by preventing or mitigating the liquid loading problem.
Common gas well deliquification methods include intermittent production, gas lift, wellhead compression, velocity strings to increase gas velocity, pumps or plungers to lift the liquid to the wellhead, and foamers. Each of these methods has its own disadvantages, including high operating and/or capital expenditures, regulatory and environmental issues and limited effectiveness in extending well lifetime. Accordingly, a gas well deliquification method that is more robust, simple, energy efficient and/or environmental friendly is highly desired.
US-A-2012/0 205 126 describes a process for dewatering a gas well that comprises using an on-site nitrogen generator that can deliver enough nitrogen to force water out of the well.
U.S. Pat. No. 5,339,905 describes a dewatering method for a gas well wherein the water level in the well is lowered by locating the lower end of a dewatering conduit below the water level in the well, and placing the upper end in fluid communication with a water exhaust line at the surface.
US-A-2012/0 247 779 discloses a method for inhibiting liquid loading, in an oilfield tubular. The method comprises treating at least part of an inner surface of the tubular to inhibit the creation of a liquid film and to promote the transport of liquid as droplets while minimising contact with said inner surface. The treatment can comprise providing at least part of the inner surface of the oilfield tubular with a hydrophobic fluoridated hydrocarbon coating comprising polymerised acrylic compounds. Some of the disadvantages of this method are the durability of such compounds in a gas well, risk of contamination, and the costs.
Also, foamers are sometimes used for gas well deliquification. For example, U.S. Pat. No. 3,172,474 discloses the use of sulphonated N-higher alkyl propionamides as foaming agents effective in removing fluids from oil or gas wells. Disadvantages of such foamers include environmental issues, risk of contamination, a need for defoaming, and that they are less suitable for gas wells with high condensate fractions. In addition, foamers have the disadvantage that their effectiveness is affected by brine salinity, condensate chemistry and temperature.